I have a UPS that I have added extra batteries. The UPS came with one 12ah, I have added 2 18ah and a 35ah. The 12ah battery failed and pulled down the voltage to 11.75, the case was hot, when I disconnected the battery it read 4.5 volts. The batteries have been in this state for at least a month. Is there any chance that the three remaining batteries might still be good?